ASA 125th Meeting Ottawa 1993 May

4pAO9. Enhancement of hydrodynamic flow noise by the regulation of air
bubbles in a turbulent water jet.

Murray S. Korman

Dept. of Phys., U.S. Naval Academy, Annapolis, MD 21402

Lawrence A. Crum

Univ. of Washington, Seattle, WA 98105

An experiment is performed to show that the near-field hydrodynamic flow
noise (generated by a submerged water jet) is enhanced when the turbulent flow
is modified to become a two-phase flow containing air bubbles. Pressure
spectra, in the band 5--5000 Hz, are measured using a digital spectral analyzer
from signals generated by a hydrophone placed at the axial and radial position
(Z=4D and R=4D) from the nozzle exit diameter, D=0.635 cm. An amplification
factor, G=(integral)p[sub two-phase][sup 2] df/(integral)p[sub
single-phase][sup 2] df, is measured as a function of the gross void fraction
(beta) of the air bubbles. Here, we measure (beta) to be the ratio of gas
volume flow rate (through the bubblemaker located at the nozzle entrance) to
the water volume flow rate, Q[sub g]/Q[sub w]. The amplification G is measured
as a function of (beta) by keeping Q[sub w] constant (the nozzle velocity
U=13.8 m/s) and varying Q[sub g]. Results show that G~(beta)[sup 2] and G~20 at
(beta)=0.0065. The mean-squared pressure fluctuation p[sup 2](identically equal
to)(integral)p[sub two-phase][sup 2] df is measured as a function of U by
keeping Q[sub g] fixed and varying Q[sub w]. Results show that p[sup 2]~U[sup
m], where m=3.6, 4.3, and 4.7 for Q[sub g]=50, 86, and 136 sccm, respectively.
[Work supported by NCPA.]